T255 Fluids and Melts in Geologic Systems (Posters)

Tuesday, 24 October 2017
9:00 AM - 6:30 PM
Halls 4EF

PROLONGED MAGMATISM WITHIN THE LITTLE COTTONWOOD STOCK: A LIKELY SOURCE OF HEAT AND FLUIDS FOR (RE)CRYSTALLIZATION WITHIN THE ALTA STOCK, WASATCH MOUNTAINS, UTAH, U.S.A

Paper number: T255-2
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

The adjacent Alta (35-33.5 Ma) and Little Cottonwood stocks (LCS; 30.5 ± 0.5 Ma) of the Wasatch Igneous Belt (WIB) were emplaced into the thickened crust of the Sevier thrust belt along a trend subparallel with the Uinta Arch. The LCS is structurally deeper, larger, and more evolved than the Alta stock. U-Pb titanite dates and Zr-in-titanite thermometry from the Alta stock margin and endoskarn indicate that high-temperature hydrothermal activity occurred in the stock margin at least intermittently from ~35-24 Ma and the associated fluid flow possibly contributed to the development of the extensive Alta contact aureole. Though this time range overlaps previous U-Pb zircon dates and two titanite dates from the LCS, more detailed information about the timing and duration of emplacement has been lacking. Five new U-Pb dates from titanite and zircon collected with LASS-ICP-MS provide a timeline of magmatic processes in the LCS. The zircon dates record crystallization at near-solidus Ti-in-zircon apparent temperatures (730 ± 50 ºC) from ~35–24 Ma at the structurally high northern margin of the LCS and ~33–28 Ma at the structurally deeper western margin. Chemical zoning within zircons correlates with variations in U-Pb date: CL bright zircon rims yield ~26–24 Ma dates while CL dark mantles and cores yield ~35–28 Ma dates. These dates likely record a variety of processes ranging from antecryst transport, syn-emplacement crystallization, and zircon crystallization from final partial melt. These data indicate complicated zircon growth and inheritance systematics suggestive of a long-lived magmatic system. U-Pb titanite dates record crystallization from ~34-27 Ma at the northern margin of the LCS and have smaller distributions. These data suggest that the Little Cottonwood stock grew upward over ~5–8 Myr from emplacement to final crystallization. These data also provide crucial insight into the possible transfer of heat and fluid from LCS interaction through the Alta contact aureole.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-308000

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